Control systems that control a load with an output voltage or an output current of constant value are known. One application of such systems is a constant voltage supply system. The control system generally includes means for providing the output voltage to the load. A feedback circuit supplies a feedback signal. A summing circuit algebraically sums the feedback current with a reference current to provide an error signal that changes as the feedback signal changes. The feedback signal serves to correct and regulate the magnitude of the output voltage delivered to the load. The error signal is processed by a voltage adjustment means including an error amplifier that amplifies the error signal for use in making an adjustment to the output voltage so as to maintain its constant value.
Control systems of this type are often subjected to relatively rapid step changes of current (transients) occurring as a result of operation of the load. This change in output load current results in an output voltage change that is fed back to the error amplifier via the summing circuit. The conventional error amplifier has a frequency compensation capacitor and series resistor in its feedback circuit that limits bandwidth and gain, with the result that control system response to such transients may be relatively slow. This can be detrimental in many applications. For example, too much drop in output voltage in cellular phone testing can result in phone shut down and an inability to test the phone properly.
One technique of addressing these load transients is to increase the gain of the error amplifier by reducing the value of a frequency compensation capacitor contained in the amplifier feedback circuit. In practice, however, this technique is of limited application since values of the capacitor which are too low will reduce stability and will result in an unstable or oscillatory control system.
Accordingly, there is a need for a control system with improved performance for handling load transients with rapid recovery times without affecting steady state operation and stability of the control system.